Astronomers get first glare-free view of Uranuss rings

Astronomers have obtained the first glare-free view of the rings of Uranus and the fine dust that permeates them.

Washington, Aug 24 : Astronomers have obtained the first glare-free view of the rings of Uranus and the fine dust that permeates them.

The rings were discovered in 1977, and as they can be seen once every 42 years, this is the first opportunity astronomers have to observe a Uranus ring crossing and perhaps to discover a new moon or two.

Using data from observations made by the Keck II telescope, the team of astronomers led by Imke de Pater of University of California, Berkeley, found that the rings of micron-sized dust had changed significantly since the Voyager 2 spacecraft photographed the Uranus system 21 years ago.

The inner rings are much more prominent than expected, revealing material in otherwise empty regions of the system of rings, said de Pater, a UC Berkeley professor of astronomy.

"People tend to think of the rings as unchanging, but our observations show that not to be the case. There are a lot of forces acting on small dust grains, so it is not that crazy to find that the arrangement of rings has changed," she said.

Using the near infrared camera (NIRC2) and adaptive optics on the Keck II telescope on May 28, the team took striking images of the nearly edge-on ring appearing as a bright line bisecting a dim Uranus, which appears dark in the infrared.

"The improvements to the adaptive optics systems allowed us to capture unbelievably crisp images of Uranus; it was as if the Keck telescope was orbiting in space," said Marcos van Dam, adaptive optics scientist at the W. M. Keck Observatory.

"The outermost ring is not visible in our infrared images. This ring is very blue, and therefore harder to see in the infrared. We may detect it when the rings are fully edge-on and when we can observe it for several hours," added co-author, Heidi B. Hammel of the Space Science Institute in Boulder, Colorado.

The scientists said that with further analysis of the Hubble data, it might be possible to detect some of the small moons, and perhaps some not seen before, that shepherd the debris into distinct rings.

"Two little satellites called Cordelia and Ophelia straddle the brightest ring, the epsilon ring, and keep it in place, but people have always assumed there must be a bunch more of these satellites that are confining the nine other narrow rings," said astronomer Mark Showalter of the SETI Institute.

"This is the unique viewing geometry that only comes along once in 42 years, when we have a chance of imaging these tiny satellites, because normally they are lost in the glare of the rings. Now, the rings are essentially invisible," he said.

Prof. de Pater said astronomers at the Very Large Telescope (VLT) in Chile, run by the European Southern Observatory (ESO), and at the Palomar Observatory in southern California operated by the California Institute of Technology, also observed Uranus during the current crossing.

The study appears online in Science. Prof. de Pater will discuss the results during a talk today at the European Planetary Science Congress 2007 meeting in Potsdam, Germany.

ANI